1. Field of the Invention
The present invention relates to monitoring a concentration of hemoglobin in a human body. More particularly, the present invention relates to a method and apparatus for noninvasively monitoring hemoglobin concentration and oxygen saturation in blood.
2. Description of the Related Art
Human blood consists of liquid plasma and three different corpuscles (i.e., red corpuscles, white corpuscles, and platelets). A primary function of the blood is to carry oxygen through the human body. Oxygen is essential to keep human body cells in a normal condition. If oxygen content is reduced, the metabolism of tissue cells is restricted. Furthermore, if oxygen is not supplied to the human body for a long time, body activity may stop. This critical oxygen supply function of the body relies essentially on the presence of hemoglobin in the red corpuscles. Accordingly, the total hemoglobin content in red corpuscles is considered to be a critical value in the clinical medicine field. Conventionally, the total hemoglobin content has been chemically analyzed by withdrawing blood from the human body. That is, hemoglobin concentration has been measured by a hemoglobincyanide method in clinical laboratories. However, a need exists for real-time monitoring of a patient""s hemoglobin concentration in operating rooms or emergency rooms. In addition, females, pregnant females, growing children, and teenagers may require occasional measurements of their hemoglobin concentration values at home. Therefore, there is a need for measuring the hemoglobin concentration noninvasively without having to withdraw blood from the body.
Conventional methods of measuring hemoglobin concentration and oxygen saturation do not consider the scattering effects that occur because hemoglobin is present in red blood cells, which act to scatter incident light. Therefore, hemoglobin concentration and oxygen saturation cannot be measured accurately by conventional methods.
In an effort to solve the problems of conventional methods, it is a first feature of an embodiment of the present invention to provide a method for noninvasively accurately monitoring hemoglobin concentration and oxygen saturation by considering light scattering by red blood cells.
It is a second feature of an embodiment of the present invention to provide an apparatus for noninvasively accurately monitoring hemoglobin concentration and oxygen saturation by the above method.
The first feature of an embodiment of the present invention provides a method for noninvasively monitoring hemoglobin concentration and oxygen saturation including: (a) selecting at least two wavelengths from a region of wavelengths in which an extinction coefficient for water is smaller than an extinction coefficient for hemoglobin, the at least two wavelengths including at least two isobestic wavelengths; (b) sequentially radiating incident light beams having the selected wavelengths onto a predetermined site of a body that includes a blood vessel; (c) receiving, at another site of the body, light beams sequentially transmitted through the predetermined site and converting the received light beams into electrical signals; (d) calculating the light attenuation variation caused by pulses of blood for the respective wavelengths from the electrical signals; (e) obtaining at least one ratio of the light attenuation variation between the selected wavelengths; and (f) calculating the hemoglobin concentration CHb in blood using the calculated at least one ratio of the light attenuation variation between the wavelengths.
The second feature of an embodiment of the present invention provides an apparatus for noninvasively monitoring hemoglobin concentration and oxygen saturation including: a light radiation unit for sequentially radiating incident light beams having at least two wavelengths selected from a region in which an extinction coefficient for water is smaller than an extinction coefficient for hemoglobin, onto a predetermined site of the body that includes a blood vessel; a photodetector unit for receiving, at another site of the body, light beams transmitted through the predetermined site, converting the received light beams into an electrical signal, and outputting the converted electrical signal; a variation calculation unit for calculating light attenuation variation for each of the selected at least two wavelengths from the electrical signal and outputting the calculated light attenuation variation; a ratio calculation unit for calculating at least one ratio among the light attenuation variations sequentially input from the variation calculation unit and outputting the calculated at least one ratio of the light attenuation variations; and a concentration calculation unit for calculating hemoglobin concentration in blood from the at least one ratio and outputting the calculated hemoglobin concentration, wherein the at least two wavelengths are externally selected to include at least two isobestic wavelengths.